VEHICLE POWDER COATING SYSTEM

Abstract: An apparatus for applying powder coating material onto large objects such as automotive, truck or other vehicle bodies (32) includes a powder spray booth (12) defining a controlled area (30) within which to apply powder coating material onto the vehicle bodies (32), a powder kitchen (14) located at a remote position from the powder spray booth (12), and a number of feed hoppers (68, 96) located proximate the booth which receive powder coating material from the powder kitchen (14) and supply it to automatically or manually manipulated powder spray guns (42, 46) associated with the spray booth (12). Oversprayed powder coating material is removed from the spray booth (12) interior by a powder collection and recovery system (16) which transmits the oversprayed powder back to the powder kitchen (14) for recirculation to the powder spray guns (42, 46).

Description: VEHICLE POWDER COATING SYSTEM Field of the Invention This invention relates to powder coating systems, and, more particularly, to a powder coating system for use in vehicle manufacturing facilities including a powder spray booth, a powder supply located remote from the booth and a powder collection and recovery system. Background of the Invention The application of coating materials to large objects such as automotive and other vehicle bodies has conventionally been accomplished in spray booths having an elongated tunnel-like construction formed with an inlet for the ingress of a vehicle body, a coating application area, a curing or drying area in some designs, and, an outlet for the egress of the vehicle body. In many systems, "conditioned" air, i.e. humidified and filtered air, is introduced by a blower or feed fan into a plenum chamber at the top of the spray booth and then directed downwardly toward the vehicle body moving through the booth. The conditioned air picks up oversprayed coating material within the booth interior and this air entrained oversprayed material is drawn downwardly through the floor or side of the booth by one or more exhaust fans. Filters are provided to capture the oversprayed coating material, and the resulting filtered or clean air is withdrawn from the booth and either exhausted to atmosphere or recirculated within the system for reuse. The coating material in most common use for vehicles such as automobiles, trucks and the like is a high solids, resinous paint material which contains a relatively high percentage of liquid solvent components to facilitate atomization of the resinous material. The problems attendant to the recovery of oversprayed, resinous paint material have been well documented and present a continuing environmental problem for the coating and finishing industry. See U.S. Patent Nos. 4,247,591 to Cobbs, et al. and 4,553,701 to Rehman, et al. As disclosed in U.S. Patent No. 5,078,084 to Shutic, et al., owned by the assignee of this invention, powder coating material has been suggested as an alternative to solvent based liquid paint materials for the coating of large objects such as vehicle bodies. In the practice of powder coating, a powdered resin is applied to the substrate and then the substrate and powder are heated so that the powder melts and when subsequently cooled, forms a solid continuous coating on the substrate. In most powder spraying applications, an electrostatic charge is applied to the sprayed powder which is directed toward a grounded object to be coated so as to increase the quantity of powder which attaches to the substrate and to assist in retaining the powder on the substrate. The application of powder material onto automotive or truck bodies is performed in a spray booth which provides a controlled area wherein oversprayed powder which is not deposited on the vehicle body can be collected. Containment of the oversprayed powder within the booth is aided by an exhaust system which creates a negative pressure within the booth interior and causes the oversprayed powder to be drawn through the booth and into a powder collection and recovery system. The recovered, oversprayed powder can be saved for future use, or is immediately recycled to powder spray guns associated with the powder spray booth. A number of problems are inherent in coating automotive and other vehicle bodies with powder coating material. Due to the design of vehicle manufacturing facilities, the source of coating material is usually positioned at a remote location from the spray booth, i.e. as much as several hundred feet. Moreover, large quantities of powder coating material, e.g. on the order of 300 pounds per hour and up, must be transferred from the source to the spray booth over this relatively long distance at flow rates such as 1 to 2 pounds per second. Additionally, the powder coating material must be transferred with the appropriate density and particle distribution in order to obtain an acceptable coating of the powder material on the vehicle bodies. The term "density" refers to the relative mixture or ratio of powder-to-air, and the term "particle distribution" refers to the disbursion of powder particles of different sizes within the flow of air entrained powder material to the spray guns associated with the powder spray booth. It has been found that currently available powder coating systems are generally incapable and/or deficient in transporting large quantities of powder material at high flow rates over long distances, while maintaining the desired density and particle distribution. As noted above, not all of the powder coating material discharged within the powder spray booth adheres to the vehicle bodies moving therethrough. This oversprayed powder material is collected by a powder collection and recovery system at the base of the booth as disclosed, for example, in Patent 5,078,084 to Shutic, et al. In systems of this type, the powder collection and recovery system includes individual groups or bank of cartridge filters each contained within a series of individual powder collection chambers mounted side-by- side beneath the floor of the spray booth. A single exhaust fan or blower creates a negative pressure within the booth interior, which draws oversprayed, air entrained powder material into each of the individual powder collection chambers where the powder is collected on the walls of the cartridge filters and "clean air" passes therethrough for eventual discharge to atmosphere. Reverse air jets are operated to dislodge the collected powder from the walls of the cartridge filters which then falls to the base of the powder collection chambers where it is removed for collection or recirculation back to the spray guns associated with the powder spray booth. In high volume applications such as coating automotive vehicle bodies, serviceability of the powder collection and recovery system, and, the application of a uniform negative pressure within the booth interior are of particular concern. It has been found somewhat difficult in certain instances to obtain a uniform negative pressure within the booth interior using a single exhaust or blower fan, which, in turn, adversely affects the efficiency with which the powder coating material can be collected and also can disrupt the pattern of powder coating material discharged from the spray guns onto the vehicle bodies moving through the booth. There has also been a need in systems of this type to improve the serviceability of the reverse air jet valves and cartridge filters contained within each powder recovery chamber. Summary of the Invention It is therefore among the objectives of this invention to provide a powder spraying system for applying powder coating material onto large objects such as automotive or other vehicle bodies which is capable of transmitting large quantities of powder material over long distances at relatively high flow rates while maintaining the desired density and particle distribution, which is capable of automatically maintaining the appropriate volume of powder coating material within the system irrespective of demand, which efficiently collects and recovers large quantities of oversprayed powder for recirculation, and, which is comparatively easy to service. These objectives are accomplished in an apparatus for applying powder coating material onto large objects such as automotive, truck or other vehicle bodies which includes a powder spray booth defining a controlled area within which to apply powder coating material onto the vehicle bodies, a "powder kitchen" located at a remote position from the powder spray booth, and, a number of feed hoppers located proximate the booth which receive powder coating material from the powder kitchen and supply it to automatically or manually manipulated powder spray guns associated with the booth. Oversprayed powder coating material is removed from the booth interior by a powder collection and recovery system which transmits the oversprayed powder back to the powder kitchen for recirculation to the powder spray guns. One aspect of this invention is predicated upon the concept of providing an efficient means for the transfer of powder coating material from a remote location, i.e. at the powder kitchen, to the feed hoppers located proximate the spray booth. This is accomplished in the apparatus of this invention by a powder transfer system which is operated using vacuum or negative pressure instead of positive pressure. The powder kitchen includes one or more primary hoppers each coupled to a powder receiver unit connected to a source of virgin powder coating material within the powder kitchen. A transfer line interconnects the primary hopper with a powder receiver unit associated with each of the feed hoppers at the spray booth. A first vacuum pump is operative to create a negative pressure within the powder receiver unit associated with the primary hopper to draw virgin powder material from the source into the powder receiver unit which, in turn, supplies powder to the primary hopper. A second vacuum pump applies a negative pressure within each powder receiver unit associated with the feed hoppers so that virgin powder material from the primary hopper located in the powder kitchen is drawn through the long transfer line into the powder receiver units associated with the feed hoppers in the vicinity of the spray booth. The powder receiver units at the spray booth fill their respective feed hoppers with powder, which, in turn, is transferred from the feed hoppers by powder pumps to powder spray guns within the spray booth. This same principal of powder transfer under the application of negative pressure is employed in the collection of oversprayed powder material from the spray booth. A reclaim hopper located in the powder kitchen is coupled to a powder receiver unit connected by a reclaim line to the powder collection and recovery system associated with the powder spray booth. A vacuum pump creates a negative pressure within the powder receiver unit associated with the reclaim hopper which receives oversprayed powder from the booth, and, in turn, transfers such oversprayed powder to the reclaim hopper. This reclaimed, oversprayed powder is then transmitted from the reclaim hopper under the application of negative pressure by another vacuum pump to supply the powder to powder receiver units associated with feed hoppers located near the booth. These feed hoppers then supply the oversprayed powder to spray guns associated with the spray booth which are operative to apply the powder to other portions of the vehicle body being coated. It has been found that large quantities of powder coating material, e.g. on the order of 300 pounds per hour and up, can be efficiently and effectively transmitted by the vacuum transfer system described above to satisfy the particular demands of automotive manufacturing facilities wherein the source of the powder coating material is located remote from the powder spray booth. It is believed that the use of vacuum, as opposed to positive pressure, uses less air and therefore reduces the overall energy requirements of the system. Additionally, in the event of a leak in one of the transfer lines extending between the powder kitchen and spray booth, the powder material is drawn inwardly within such transfer lines because of the vacuum therein instead of being forced outwardly as would be the case with a positive pressure powder transfer system. This reduces the risk of contamination of the facility with powder in the event of a leakage problem. Another feature related to the powder transfer aspect of this invention involves the automatic monitoring and replenishment of virgin powder coating material and oversprayed powder material as the coating operation proceeds. Each of the primary hoppers, reclaim hoppers and feed hoppers is carried by a load cell connected to a programmable logic controller. These load cells are set on a zero reference with the empty weight of their respective hoppers, and are effective to measure the weight of powder material which enters each individual hopper during operation of the system. Considering a primary hopper, for example, the load cell associated therewith sends a signal to the controller indicative of the weight of powder within such primary hopper during operation of the system. In the event the quantity of powder material within the primary hopper falls beneath a predetermined minimum, the controller receives a signal from the load cell and operates the vacuum pump connected to the powder receiver unit associated with such primary hopper so that additional, virgin powder coating material is transmitted from the source, into the powder receiver unit and then to the primary hopper. Once that primary hopper receives a sufficient level of powder coating material, further supply of powder is terminated. The reclaim hopper and feed hoppers operate in the same manner so that appropriate levels of powder coating material are maintained in each during a powder coating operation. Additionally, a connector line is provided between each primary hopper and reclaim hopper so that virgin powder coating material can be supplied from the primary hoppers to the reclaim hoppers in the event the quantity of oversprayed powder material collected within the powder collection and recovery system of the spray booth is insufficient to maintain the quantity of powder material within the reclaim hoppers at the desired level. Another aspect of this invention involves the provision of structure within each of the primary hoppers, reclaim hoppers and feed hoppers to ensure that the powder coating material is transferred within the system, and supplied to the spray guns, with the desired density and particle distribution. In this respect, principals of operation similar to those employed in the powder feed hopper disclosed in U.S. Patent No. 5,018,909 to Crum, et al., owned by the assignee of this invention, are used in the various hoppers of this invention. Generally, each of the hoppers herein include a porous plate which receives an upward flow of air directed through baffles located within an air plenum in the base portion of such hoppers. Agitators, including rotating paddles or blades, are located above the porous plate to ensure that the powder material is properly fluidized, has a homogeneous distribution of powder particles and has the appropriate density or air-to-particle ratio prior to discharge from the respective hoppers. A still further aspect of this invention is predicated upon the concept of providing an efficient, easily serviceable powder collection and recovery system for the powder spray booth, which produces a uniform, downwardly directed flow of air within the booth interior. The powder collection and recovery system herein is modular in construction including a number of powder collection units mounted side-by-side along the length of the powder spray booth beneath its floor. Each of the powder collection units includes a powder collection chamber housing two groups or banks of cartridge filters mounted in an inverted V shape above an angled, fluidizing plate located at the base of the powder collection chamber. A limited number of individual powder collection units are connected by a common duct to a separate exhaust fan or blower unit. Each exhaust fan is effective to create a negative pressure within its associated powder collection units to draw air entrained, oversprayed powder material from the booth interior, downwardly through the floor of the booth and then into each of the powder collection chambers. The oversprayed powder material collects on the walls of the cartridge filters and "clean" air passes therethrough into clean air chambers associated with each powder collection unit. Pulsed jets of air are periodically introduced into the interior of the cartridge filters from air jet valves positioned thereabove to dislodge powder collected on the walls of the filters which then falls onto the angled fluidizing plate at the base of each powder collection chamber for removal. Each powder collection chamber has an outlet connected to a common header pipe, and a gate valve is positioned in each of these outlet lines. The system controller is effective to sequentially open and close the gate valves so that collected powder material is removed from the various powder collection units in sequence for transfer to the reclaim hopper associated with the powder kitchen. The construction of the powder collection and recovery system herein provides a number of advantages. Because a number of exhaust or blower units are employed, each associated with a limited number of powder collection units, a more uniform and evenly distributed 16 Description of the Drawings The structure operation and advantages of the presently preferred embodiment of this invention will become further apparent upon consideration of the following description, taken in conjunction with the accompanying drawings, wherein: Fig. 1 is a partial schematic view of one end of the powder spray booth including feed hoppers and a portion of the powder collection recovery system, and including a schematic depiction of the powder kitchen; Fig. 2 is an elevational view of a powder receiver unit and primary hopper contained within the powder kitchen; Fig. 3 is a plan view of the primary hopper shown in Fig. 1; Fig. 4 is a cross-sectional view taken generally along line 4-4 of Fig. 3; Fig. 5 is an elevational view in partial cross- section of a feed hopper of this invention; Fig. 6 is a schematic, partially cut-away view of a robot hopper of this invention; Fig. 7 is a schematic, partially cut-away view of the powder collection and recovery system herein; 15 downward flow of air is created within the interior of the powder spray booth along its entire length. This is an improvement over systems having a single exhaust fan or blower because it has proven difficult to obtain a uniform negative pressure within a spray booth having the extreme length required to coat large objects such as vehicle bodies with only one blower unit. Servicing of the powder collection and recovery system herein is also made much easier than in prior designs. The reverse air jet valves are located at the top of the powder collection units for easy access, and the cartridge filters are easily removed from the powder collection chambers by one operator. Removal of powder material from each of the powder collection chambers is also made easier by the angled, fluidizing plate at the base thereof which aids in smoothly transferring powder out of the chambers. Additionally, the walls of the powder collection chamber are made sufficiently thin so that they are vibrated when the reverse jets of air are activated to assist in the transfer of powder onto the porous plate. Fig. 8 is an end view of a powder collection chamber; and Fig. 9 is a side view of the powder collection chamber depicted in Fig. 8. Detailed Description of the Invention Referring now to the Figs., the powder coating system 10 includes a powder spray booth 12, devices for transferring powder coating material from a powder kitchen 14 to the booth 12, and, a powder collection and recovery system 16 associated with the booth 12. These system elements are described separately below, including a discussion of the operation of each. Powder Spray Booth Referring to Figs. 1 and 2, the powder spray booth 12 includes a ceiling 18, floor 20, opposed side walls 22, 24 and opposed end walls defining a booth inlet 26 and a booth outlet 28. See also Fig. 7. This construction of spray booth 12 defines an interior 30 forming a controlled area in which to apply powder coating material onto objects such as a vehicle body 32 moved by a conveyor 34 through the longitudinally extending center portion 36 of the spray booth 12. Oversprayed powder material which does not adhere to the vehicle body 32 passes through gratings 38 located along the floor 20 of spray booth 12 and into the powder collection and recovery system 16 described in detail below. The powder spray booth 12 extends for a substantial longitudinal distance, and can be provided with a variety of powder spray guns positioned at different locations therealong so that all areas of the vehicle body 32 are coated with powder coating material in the course of passage through the booth interior 30. For purposes of illustration, a robot 40 carrying a spray gun 42 is depicted on one side of the spray booth 12, and an overhead gun manipulator 44 is illustrated in position above the vehicle body 32 carrying spray guns 46. Depending upon the size of the vehicle body 32, the types of powder coating material to be applied thereto, the desired areas of coverage on the vehicle body 32 and other factors, essentially any number of spray guns manipulated either automatically or manually can be provided along the length of the spray booth 12 for covering the vehicle body 32 with powder coating material. The particular location and operation of such spray guns forms no part of this invention of itself, and is therefore not discussed herein. In the presently preferred embodiment, the vehicle body 32 is held at ground potential by the conveyor 34 and an electrostatic charge is imparted to the powder coating material by the spray guns 42 and 46. The electrostatic charge applied to the powder material increases the quantity of powder which adheres to the vehicle body 32, and assists in retaining powder thereon, but a relatively large quantity of powder material is nevertheless "oversprayed", i.e. fails to adhere to the vehicle body 32. This oversprayed powder must be collected and recovered in the course of the powder coating operation, as described below. Powder Transfer System An important aspect of this invention involves the structure of system 10 for transferring the powder coating material from the powder kitchen 14 to the spray booth 12. In many vehicle manufacturing facilities, the powder kitchen 14 is positioned at a remote location from the spray booth 12, e.g. several hundred feet away, and a large quantity of powder coating material must be rapidly transmitted therebetween. Powder flow rates of 1-2 pounds per second, and total demand for powder of 300 pounds per hour and up, are not uncommon. The overall configuration of the powder transfer system of this invention which is capable of efficiently and economically satisfying such parameters is described first, followed by a detailed discussion of the various separate elements making up such transfer system. The powder kitchen 14 is essentially a closed housing (not shown) which is provided with "conditioned" air, i.e. filtered and humidified air, supplied from an air house (not shown) of conventional design. Within the powder kitchen 14 is a source 54 housing virgin powder coating material, which is connected by a line 56 to a first powder receiver unit 58 described in detail below. The powder receiver unit 58 is connected to a primary hopper 60, and by a suction hose 61 to a first vacuum pump 62, both of which are housed in the powder kitchen 14. The primary hopper 60 is connected by a transfer line 64 to a second powder receiver 66 coupled to a first feed hopper 68. This transfer line 64 carries a first gate valve 70, and is connected to a first makeup air valve 72, both located downstream from the primary hopper 60 and within the powder kitchen 14. The makeup air valve 72 is connected to a pressurized air source 73, depicted schematically in Fig. 1. As shown at the top of Fig. 1, the second powder receiver 66 and first feed hopper 68 are located proximate to the powder spray booth 12, but the transfer line 64 interconnecting the primary hopper 60 and second powder receiver 66 may be several hundred feet in length. The feed hopper 68 is connected by a line 67 to a third vacuum pump 69 housed within the powder kitchen 14, and carries a powder pump 74 (See Fig. 5) which is connected by a line 76 to a robot hopper 78. The robot hopper 78, in turn, is connected by a line 79 to the spray gun(s) 42 associated with robot 40. The right hand portion of powder kitchen 14, as depicted in Fig. 1, contains similar structure to that described above in connection with primary hopper 60. Instead of receiving virgin powder coating material from container 54, this portion of the powder kitchen 14 is primarily supplied with collected, oversprayed powder from the collection and recovery system 16 of powder spray booth 12. In the presently preferred embodiment, the powder kitchen 14 houses a reclaim hopper 80 coupled to a third powder receiver unit 82 of the same type as receiver units 58 and 66. The third powder receiver unit 82 is connected by a line 83 to a third vacuum pump 84 located within the powder kitchen 14, and is joined by a reclaim suction line 86 to the powder collection and recovery system 16 as discussed below. A second transfer line 88, carrying a gate valve 90 and makeup air valve 92 connected to air source 73, interconnects the reclaim hopper 80 with a fourth powder receiver unit 94. This fourth powder receiver unit 94 is coupled to a second feed hopper 96 located proximate the powder spray booth 12. As schematically depicted in Figs. 1 and 5, the second feed hopper 96 includes a positive pressure powder pump 98 which supplies powder material through a line 100 to the spray guns 46 associated with overhead gun manipulator 4 . The fourth powder receiver unit 94 is connected to a fourth vacuum pump 102, located within the powder kitchen 14, by a line 104. In the presently preferred embodiment, the primary hopper 60, first feed hopper 68, robot hopper 78, reclaim hopper 80 and second feed hopper 96 are each carried by an individual load cell 106A-E, respectively, of the type commercially available under Model Nos. FLB- 3672-1K and H1242 PS-C500 from the Hardy Instruments Company. The load cells 106A-E are "zeroed" or adjusted to reflect a zero weight when each of their associated hoppers are empty of powder coating material. As discussed below, each load cell 106A-E is operative to measure the weight or quantity of powder coating material deposited in their associated hoppers and produce a signal representative of such weight reading. These signals are transmitted to a Programmable Logic Controller 108 (PLC) , preferably of the type commercially available from Allen Bradley of Cleveland, Ohio, under Model No. PLC-5. The controller 108, in turn, operates each of the vacuum pumps 62, 71, 84 and 102, as well as valves 70, 72, 90 and 92, in response to the signals from load cells 106A-E. Operation of Powder Transfer System A detailed discussion of the structure and operation of each individual element of the powder transfer system is given below, but its overall operation can be described with reference to the schematic representation of Fig. 1. Unlike many prior systems, the powder transfer system of this invention employs negative pressure to transmit the powder coating material from the powder kitchen 14 to the powder spray booth 12. Additionally, the supply and transfer of powder is accomplished essentially automatically as the powder coating operation proceeds. Referring initially to the left hand portion of the powder kitchen 14, virgin powder coating material is transferred from the source 54 when the controller 108 activates the first vacuum pump 62. The first vacuum pump 62 creates a negative pressure within the first powder receiver 58 which, in turn, draws the virgin powder coating material from source 54 through line 56 into the first powder receiver 58. As described below, the first powder receiver 58 discharges powder coating material into the primary hopper 60, and the quantity of such powder coating material received is monitored by the load cell 106A associated with primary hopper 60. When a predetermined level or quantity of powder coating material is present within primary hopper 60, its load cell 106A sends a signal representative of this condition to the controller 108, which, in turn, deactivates the first vacuum pump 62. The transfer of powder coating material from primary hopper 60 to the first feed hopper 68 is also accomplished under the application of negative pressure. The controller 108 activates the second vacuum pump 69 to create a negative pressure within the second powder receiver 66 associated with first feed hopper 68. This negative pressure draws powder coating material from the primary hopper 60 into transfer line 64, and through the gate valve 70 therein which is opened by controller 108 simultaneously with the activation of second vacuum pump 69. The transfer of powder from primary hopper 60 is monitored by its load cell 106A which sends a signal to controller 108 when a predetermined quantity or weight of powder is emitted from primary hopper 60. The controller 108, in turn, closes the gate valve 70 within transfer line 64 to stop the flow of powder therethrough and turns off the second vacuum pump 69. Filling of the first feed hopper 68 with powder from the primary hopper 60 is accomplished by monitoring the weight or quantity of powder therein by its associated load cell 106B. When the quantity of powder in first feed hopper 68 falls below a predetermined level, its load cell.106B sends a signal to controller 108 to activate a metering device contained within the second powder receiver 66, as discussed in detail below. The powder transferred from primary hopper 60 to the second powder receiver 66 is then directed into th first feed hopper 68 until a predetermined weight is obtained therein, at which time a signal from load cell 106B to controller 108 causes the metering device within second powder receiver 66 to cease operation. As schematically depicted at the top of Fig. 1, the powder coating material within the first feed hopper 68 is removed by the powder pump 74 (see also Fig. 5) , under the application of positive pressure, and transmitted via line 76 into the robot hopper 78 carried by its own load cell 106C. Once the robot hopper 78 receives a sufficient quantity of powder coating material, as monitored by load cell 106C, the powder pump 74 is deactivated by controller 108 and a second powder pump 77 transfers the powder coating material from robot hopper 78 via line 79 to the spray guns 42 associated with robot 40 for application onto the vehicle body 32. The purpose of the load cells 106A-E is to provide for essentially automatic operation of the system 10 so that the flow rate and total quantity of powder coating material being transferred through the system keeps pace with the demand as a given number of vehicle bodies 32 pass through the powder spray booth 12. The load cells 106A-C associated with primary hopper 60, first feed hopper 68 and robot hopper 78, respectively, are each operative to monitor the quantity or weight of powder coating material therein and provide a signal to the controller 108 in the event the quantity of powder falls below a predetermined level. When the controller 108 receives such signals, the appropriate vacuum pump or metering device is activated to transfer powder coating material into the hopper(s) whose supply of coating material has been depleted. In this manner, all of the hoppers 60, 68 and 78 have a continuous, adequate supply of powder coating material. Because of the extreme length of transfer line 64, the powder kitchen 14 includes a valving arrangement to avoid the presence of residual powder coating material within transfer line 64 when the second vacuum pump 69 is turned off to stop the flow of powder coating material from the primary hopper 60 to the second powder receiver 66. As noted above, during the transfer operation from primary hopper 60 through second powder receiver 66, the controller 108 opens gate valve 70 within transfer line 64. When the load cell 106A associated with primary hopper 60 indicates a predetermined quantity of powder has been emitted therefrom, the controller 108 deactivates second vacuum pump 69, closes gate valve 70 and opens makeup air valve 72 within the powder kitchen 14. Pressurized air from the air source 73 then enters the transfer line 64 through makeup air valve 72 to "chase" or positively force the coating material which remains in transfer line 64 upstream from the powder kitchen 14 into the second powder receiver 66. This substantially prevents any accumulation of powder coating material within the transfer line 64 so that subsequent transfer operations of powder from the primary hopper 60 to the first feed hopper 68 can be performed quickly and efficiently. With reference to the right hand portion of the powder kitchen 14, and top right hand portion of Fig. 1, the components of the powder transfer system which supply powder coating material to the spray guns 46 are depicted. As discussed above, such elements include the reclaim hopper 80, third powder receiver 82 and third and fourth vacuum pumps 84, 102 within the powder kitchen 14; and, the fourth powder receiver 94, second feed hopper 96 and third powder pump 98 located proximate the powder spray booth 12. The structure and operation of these elements is essentially identical to their counterparts on the left hand portion of Fig. 1, except that instead of transmitting solely virgin powder coating material from the powder kitchen 14 to the spray booth 12 such elements transmit primarily collected, oversprayed powder coating material received from the collection and recovery system 16. In order to fill the reclaim hopper 80 with oversprayed powder material, the third vacuum pump 84 is activated by controller 108 which creates a negative pressure within third powder receiver 82 to draw powder coating material via reclaim line 86 from the collection and recovery system 16 into the third powder receiver 82. In a manner fully discussed below, the third powder receiver 82 deposits the oversprayed powder material into the reclaim hopper 80. The quantity of the powder entering the reclaim hopper 80 is monitored by load cell 106D associated therewith. From the reclaim hopper 80, the powder material is transferred to the fourth powder receiver 94 and second feed hopper 96 when the controller 108 activates fourth vacuum pump 102. The negative pressure created within the fourth powder receiver 94 pulls powder from the reclaim hopper 80 into second transfer line 88, through the gate valve 90 opened by controller 108, and into the interior of fourth powder receiver 94. The second feed hopper 96 receives such powder from the fourth powder receiver 94, the quantity of which is monitored by load cell 106E associated therewith, and the positive pressure powder pump 98 subsequently transfers the powder from second feed hopper 96 through line 100 to the spray guns 46 carried by gun manipulator 44. The operation of vacuum pumps 84 and 102, and the metering device associated with fourth powder receiver 94, is governed by the controller 108 in the same manner as discussed above, i.e. in response to signals from the load cells 106D and 106E associated with the reclaim hopper 80 and second feed hopper 96, respectively. The operation of the positive pressure powder pump 98 is also governed by controller 108 depending upon the presence of vehicle bodies 32 within the powder spray booth 12. Valves 90 and 92 within the powder kitchen 14 function in the identical manner as valves 70 and 72 described above. Before discussing each of the individual elements associated with the powder transfer system in detail, two additional features of the powder transfer system should be noted. It is contemplated that in some applications the total quantity of powder coating material required from the reclaim hopper 80 may exceed the amount of oversprayed, powder coating material supplied thereto by the collection and recovery system 16. In order to ensure that a sufficient quantity of powder coating material is always present within reclaim hopper 80, the primary hopper 60 containing virgin powder coating material includes a powder pump 110 connected by a line 112 to a minicyclone 114 carried by the reclaim hopper 80. This minicyclone 114 is commercially available from Nordson Corporation of Amherst, Ohio under Model No. PC-4-2. In the event the load cell 106D associated with reclaim hopper 80 senses less than the required weight of powder material within reclaim hopper 80, and sufficient powder cannot be supplied from the collection and recovery system 16, then the controller 108 activates powder pump 110 to transfer virgin powder coating material through line 112 and minicyclone 114 into the reclaim hopper 80 to supplement the total amount of powder therein. If such transfer is required, both virgin powder coating material and oversprayed, collected powder coating material from the booth 12 are intermixed within the reclaim hopper 80 and subsequently supplied to the spray guns 46 in the manner described above. One further aspect of the powder transfer system of this invention involves the utilization of a vent utility collector 116 located within the powder kitchen 14 which is connected by a line 118 to a vent 120 at the top of primary hopper 60. Similarly, a second vent utility collector 122, also contained within the powder kitchen 14, is connected by a line 124 to the vent 126 of reclaim hopper 80. Each of the vent utility collectors 116, 122 is operative to provide ventilation to the interior of the primary and reclaim hoppers 60, 82, respectively, and to remove "fines" from the upper portion of the interior of such hoppers 60, 82. The term "fines" as used herein refers to very small diameter particles of powder material which usually concentrate near the upper portion of powder supply hoppers and are so small that they often do not become electrostatically charged when emitted from spray guns such as spray guns 42 and 46. If they do not become charged, such small particles are not attracted to the surface of an article to be coated and therefore tend to collect within the system which reduces transfer efficiency, i.e. the proportion of particles which adhere to an article to be coated. These small particles or fines are therefore advantageously removed by the vent utility collectors 116 and 122 within the powder kitchen 14 for subsequent disposal. Having described the overall structure and operation of the powder transfer system of this invention, the individual elements mentioned above are described in detail with reference to Figs. 2-6. Powder Receivers Referring to Fig. 2, the powder receiver 58 mentioned above is illustrated in detail. It should be understood that each of the other powder receivers 66, 82 and 94 are structurally and functionally identical to powder receiver 58, and therefore only one of the powder receivers is discussed in detail herein. The powder receiver 58 includes a collector housing 128 having a hollow interior 130 within which a cartridge filter 132 is mounted by a plate 134. An access panel 136 is releasably secured by latches 138 along one side of the collector housing 128 to permit access to the cartridge filter 132. The interior 130 of collector housing 128 is vented by a vent 140, and its upper end is closed by a cap 142 secured thereto by latches 144. The cap 142 mounts a reverse air jet valve 146 in alignment with the open end of cartridge filter 132 connected to plate 134. The reverse air jet valve 146 is connected by a line 148 to an accumulator 150 which, in turn, is connected to the source 73 of pressurized air depicted schematically in Fig. 2. The cap 142 also carries a fitting 154 connected to a suction hose or line 61 from the first vacuum pump 62. The lower portion of collector housing 128 includes a powder inlet 158 connected to the line 56 from the container 54 carrying virgin powder coating material. The collector housing 128 tapers radially inwardly from the powder inlet 158, in a downward direction as depicted in Fig. 2, forming a tapered base portion 160 which includes external flanges 162. As discussed above, in order for the load cell 106A associated with primary hopper 60 to function properly it must be "zeroed" or set at a zero weight reading with the primary hopper 60 completely empty of powder coating material. In this manner, only the powder coating material which actually enters the primary hopper 60 is weighed by the load cell 106A. In order to ensure an accurate weight reading of the powder is obtained within primary hopper 60, all of the elements associated with the first powder receiver unit 58 are supported independently of the primary hopper 60 upon a frame 164 depicted in Fig. 2. This frame 164 includes a top plate 166 supported on vertical legs 168, angled braces 170 extending between the top plate 166 and vertical legs 168, and, one or more horizontal supports 172 located at intermediate positions in between the vertical legs 168. The collector housing 128 is mounted to the top plate 166 of frame 164 by bolts 174 extending between the external flange 162 of collector housing 128 and the top plate 166. Extending downwardly from the tapered base portion 160 of collector housing 128 is a flexible sleeve 176 which couples the collector housing 128 with a rotary air lock metering device 178 of the type commercially available from Premier Pneumatics, Inc. of Salina, Kansas under Model No. MDR-F-G-76-10NH-2-RT-CHE-T3. The metering device 178 is drivingly connected by a belt (not shown) to the output of a motor 182 carried on a support plate 184 connected to one of the vertical legs 168. The motor 182 is operative to rotate a series of internal vanes 186 within the metering device 178 which transfer a etered quantity of powder coating material from the tapered base portion 160 of collector housing 128 into a rotary sieve 196 mounted on a horizontal support 172. The rotary sieve 196 is a commercially available item of the type manufactured and sold by Azo Incorporated of Germany under Model No. E-240. The rotary sieve 196, in turn, transfers the powder coating material through a second flexible sleeve 198 into the powder inlet 200 of primary hopper 60 which is shown in more detail in Fig. 3 and described below. In operation, the first vacuum pump 62 is activated by controller 108 drawing a vacuum along suction hose or line 61 to create a negative pressure within the hollow interior 130 of collector housing 128. In turn, virgin powder coating material is drawn from the supply container 54 through line 56 and powder inlet 158 into the hollow interior 130 of collector housing 128. Some of the powder coating material falls by gravity into the tapered base portion 160 of collector housing 128, and another portion of the powder coating material collects on the walls of the cartridge filter 132. Periodically, pressurized air supplied from the accumulator 150 is transmitted in pulses through the reverse air jet valve 146 aligned with cartridge filter 132. These jets of air dislodge the powder coating material collected on the walls of filter 132 allowing it to fall downwardly into the tapered base portion 160 of collector housing 128. The powder coating material is transferred from the collector housing 128 by the air lock metering device 178, in response to operation of motor 182, such that a metered quantity of powder coating material enters the rotary sieve 196. After passing through the rotary sieve 196, the powder coating material falls by gravity through the flexible sleeve 198 and into the powder inlet 200 of the primary hopper 60. When a predetermined quantity of powder coating material is collected within primary hopper 60, the load cell 106A associated therewith sends a signal to the controller 108, which, in turn, discontinues operation of the first vacuum pump 62. As mentioned above, all of the other powder receiver units 66, 82 and 94 in the powder transfer system herein are structurally and functionally identical. Primary and Reclaim Hoppers The primary hopper 60 and reclaim hopper 80 are essentially identical to one another, and, for purposes of discussion, only the primary hopper 60 is illustrated and described in detail. With reference to Figs. 3 and 4, the primary hopper 60 comprises a housing 202 having an internal wall 204 in the general shape of a "figure 8". As such, the internal wall 204 includes two circular-shaped portions 206 and 208 which meet at a reduced diameter area 210 at the center of housing 202 defined by opposed, triangular-shaped baffles 212 and 214 each connected to one side of the housing 202. Each of the baffles 212, 214 have a pair of side panels 216, 218 which extend inwardly from a wall of the housing 202 and meet to form an apex 220 toward the center of the housing interior 203. As best shown in Fig. 4, a porous plate 222 is carried by mounts 224 near the base of housing 202 which separates the housing interior 203 into a fluidized bed 226 located between the porous plate 222 and the top wall 228 of housing 202, and an air plenum 230 located between the porous plate 222 and the bottom wall 232 of the housing 202. The air plenum 230 contains a number of baffles 270 and a generally U-shaped, perforated air tube 272. The bottom wall 232 rests atop the load cell 106A, discussed above in connection with the powder transfer system of this invention. The top wall 228 of housing 202 supports a first agitator 234, a second agitator 236 and an access cover 238 having a handle 240 and latch mechanisms 242 which is mounted by a hinge 243 over an opening 244 in the top wall 228. This opening 244 is offset from the powder inlet 200 of primary hopper 60 so that access to in housing interior 203 for maintenance or the like can be obtained without interference with the powder inlet 200. The first agitator 234 includes a motor 246 connected by a shaft 248 to a gear box 250. The output of gear box 250 is drivingly connected to a shaft 252 encased within a tube 254. The lower end of shaft 252 mounts at least two agitator paddles 256 which are rotatable within the circular portion 206 of the housing interior 203 formed by internal wall 204, at a location vertically above the porous plate 222. The second agitator 236 has a similar construction to first agitator 234. Second agitator 236 includes a motor 258 having a shaft 260 connected to a gear box 262 whose output is drivingly connected to a shaft 264 encased within a tube 266. Two or more paddles 268 are mounted at the base of shaft 264 within the other circular portion 208 of housing interior 203 formed by internal wall 204. As depicted in Fig. 4, the shaft 264 and tube 266 associated with second agitator 236 are slightly longer than their counterparts in the first agitator 234 so that the paddles 268 of second agitator 236 are located closer to the porous plate 222 than those of first agitator 234. The paddles 256, 268 overlap but do not interfere with one another because of the vertical offset. As mentioned above, one aspect of this invention is to provide for the transfer of large quantities of powder coating material e.g. on the order of 300 pounds per hour and up, at flow rates of 1-2 pounds per second, while maintaining the desired density and particle distribution within the flow of powder coating material. As noted above, the term "density" refers to the relative mixture or ratio of powder to air, and the term "particle distribution" refers to the disbursion of powder particles of different sizes within the flow of powder coating material. The primary hopper 60 and reclaim hopper 80 are designed to meet the desired density and particle distribution requirements at high throughputs of powder coating material. In operation, pressurized air is introduced into the perforated air tube 272 within air plenum 230 creating an upward flow of air which is evenly distributed by the baffles 270 across the bottom of porous plate 222. Powder coating material is introduced into the housing interior 203 through its powder inlet 200 and distributed along the porous plate 222 by the upward, fluidizing air flow therethrough and by operation of the first and second agitators 234, 236. The "figure 8" shape of the housing interior 203 defined by internal wall 204 substantially eliminates "dead spots" therein as the agitator paddles 256, 268 move relative to the porous plate 222 so that the powder coating material is evenly distributed along the entire surface area of porous plate 222 and agglomeration or bunching up of the powder material is substantially eliminated. This produces an even, uniform powder distribution within the fluidized bed 226 having the desired particle distribution and density. In response to activation of the third vacuum pump 69, air entrained, powder coating material is withdrawn from the housing 202 of primary hopper 60 through a suction tube 274 inserted within the housing interior 203, which, in turn, is connected to transfer line 64 described above. Feed Hoppers The first and second feed hoppers 68 and 96 are essentially identical in construction and therefore only the details of first feed hopper 68 are discussed herein. With reference to Fig. 5, feed hopper 68 comprises a housing 276 having a top wall 278 formed with an opening closed by a cover 279, a substantially cylindrical-shaped side wall 280 and a bottom wall 282 carried by the load cell 106B. The housing 276 defines an interior which is separated into essentially three discreet areas. One area is a fluidized bed 284 extending between the top wall 278 and a porous plate 286 which extends outwardly from the housing side wall 280 and is supported thereto by brackets 288. A second area within the housing 276 is air plenum 290 which extends between the porous plate 286 and a circular mounting plate 292 carried by brackets 294 mounted to the side wall 280. The third area within the interior of housing 276 is a motor chamber 296 extending between the mounting plate 292 and bottom wall 282. The feed hopper 68 is provided with an agitator 298 which includes a motor 300 carried within the motor chamber 296 by a motor mount 302 connected to the mounting plate 292. The output of motor 300 is drivingly connected to a shaft 304 rotatably carried within a bearing 306. The bearing 306 is mounted by a bearing mount 308 to the mounting plate 292 and extends vertically upwardly through the air plenum 290 to a point immediately above the porous plate 286. At least two paddles 308 are secured by a lock nut 310 at the top of shaft 304 which extends through bearing 306, so that in response to operation of motor 300 the paddles 308 are rotated with respect to the porous plate 286 at a location immediately thereabove. At least two air inlets 312, carried by mounting plate 292, are connected by tubes 314 to an air supply line 316, in a manner not shown, which enters one side of the motor chamber 296. This air supply line 316, in turn, is connected to the source of pressurized air 73 described above in connection with the powder receivers. An upwardly directed flow of air is provided through the air inlets 312 into the air plenum 290 where the air is deflected by baffles 318 mounted to the bearing 306. The purpose of these baffles is fully disclosed in U.S. Patent No. 5,018,909, owned by the assignee of this invention, the disclosure of which is incorporated by reference in its entirety herein. In operation, powder coating material is introduced into the fluidized bed 284 of housing 276 through a tapered, powder inlet 320 mounted along the side wall 280 of housing 276. The motor 300 is operative to rotate paddles 308 so that the powder coating material is evenly distributed along the porous plate 286 with no dead spots. The powder coating material is fluidized along the porous plate 286 by the upwardly directed flow of air from air supply line 316 and air inlets 312. In order to remove the powder coating material from housing 276, one or more powder pumps such as pump 74 is operated to draw the powder coating material through a suction tube 322 which extends into the housing interior immediately above the porous plate 286. A number of suction tubes 322 are shown in Fig. 5 for purposes of illustrating that multiple powder pumps 74 could be employed to draw powder from feed hopper 68. Robot Hopper The robot hopper 78 schematically depicted in Fig. 1 is shown in more detail in Fig. 6. In the presently preferred embodiment, the robot hopper 78 includes a cylindrical base forming a combined air plenum and motor chamber 324 which houses a motor 326 drivingly connected to a shaft 328 whose upper end mounts one or more paddles 330. The top portion of robot hopper 78 includes a cylindrical housing 332 having a top wall 334 and a bottom wall formed by a porous plate 336 which communicates with the air plenum and motor chamber 324. The cylindrical housing 332 defines a fluidized bed 338 within which a rectangular-shaped plate or baffle 340 is mounted. The baffle 340 is vertically spaced above the porous plate 336 and divides the fluidized bed 338 into two sections. In one section or side of baffle 340, powder coating material from feed hopper 68 is introduced through a powder inlet 342 schematically depicted at the top of the cylindrical housing 332. A suction tube 344 associated with the powder pump 79 is mounted to cylindrical housing 332 on the opposite side of baffle 340, and this suction tube 344 terminates immediately above the porous plate 336. The robot hopper 78 receives powder coating material via line 76 from powder pump 74 associated with feed hopper 68. The powder coating material enters the powder inlet 342 of cylindrical housing 332 and is directed downwardly along one side of baffle 340 onto the porous plate 336. The motor 326 is operative to rotate paddles 330 immediately above the porous plate 336 so that a uniform flow of air entrained powder material can be withdrawn by the powder pump 79 through suction tube 344 for transmission to the robot 40 and its associated spray guns 42. It has been found that the presence of baffle 340 within the interior of cylindrical housing 332 assists in stabilizing the fluidization of powder coating material across the porous plate 336 to ensure that the desired density and powder distribution within the flow of powder coating material withdrawn by powder pump 79 is maintained. Powder Collection and Recovery System With reference to Figs. 1 and 7-9, the powder collection and recovery system 16 is illustrated in further detail. This system 16 is generally related to that disclosed in U.S. Patent No. 5,078,084 to Shutic, et al. , the disclosure of which is incorporated by reference in its entirety herein. As noted above, the powder collection and recovery system 16 is located below the floor 20 of powder spray booth 12 on either side of the center portion 36 of booth 12 along which the vehicle bodies 32 are transported by conveyor 34. As depicted at the left hand portion of Fig. 7, gratings 38 cover the booth floor 20 so that oversprayed, air entrained powder coating material can be drawn downwardly from any area within the booth interior 30 into the system 16. The powder collection and recovery 16 is modular in construction and generally comprises a series of powder collection units 346 mounted side-by-side and extending longitudinally along the entire length of the booth 12. See center of Fig. 7. The powder collection units 346 are connected in groups of three or four, for example, to individual fan or blower units 348 located beneath the powder collection units 346, as shown in Fig. 1 and the right side of Fig. 7. Each of the powder collection units 346 includes a collector housing 350 having opposed side walls 354, 356, opposed end walls 358, 360 and an angled or sloped bottom wall 362. A clean air chamber 364 is located at the top of collector housing 350 which is formed by a pair of inwardly angled support plates 366, 367 each having a number of spaced openings 368, opposed side plates 369, 370, and, a pair of access doors 371, 372 which are hinged to the side plates 369, 370, respectively. The clean air chamber 364 extends across the length of collector housing 350 and connects to an extension 373, the purpose of which is described below. The lower portion of collector housing 50 forms a powder collection chamber 374 having tapered sidewalls and a bottom wall defined by a porous plate 376. The porous plate 376 is mounted above the base 362 of collector housing 350, at an angle of approximately five degrees with respect to horizontal, which forms an air plenum 377 therebetween. An upwardly directive flow of air is introduced into the air plenum 377 beneath the porous plate 376 through an inlet (not shown) so that powder coating material entering the powder collection chamber 374 is fluidized atop the porous plate 376. In the presently preferred embodiment, two groups or banks of cartridge filters 378 are located within the powder collection chamber 374 and are arranged in an inverted V shape as seen in Fig. 8. The open top of each cartridge filter 378 is carried by one of the support plates 366, 367 of clean air chamber 364 in position over an opening 368 in such plates 366, 367. Each cartridge filter 378 has a central rod 382 threaded at its upper end to receive a mount 384 which is tightened down on the rod 382 such that one of the support plates 366 or 367 is sandwiched between the mount 384 and the top of a cartridge filter 378. Preferably, one or more filter mounting plates 386 extending between end walls 358, 360 of collector housing 350 provide additional support for each cartridge filter 378. In order to dislodge powder coating material from the walls of the cartridge filters 378, which enters the collector housing 350 as discussed below, a set or group of air jet nozzles 392 is provided for each bank of cartridge filters 378. One set of air jet nozzles 392 is carried on a nozzle support 394 mounted within clean air chamber 364, and the second set of air jet nozzles 392 is carried on a nozzle support 396 within the clean air chamber 364. As depicted in Fig. 8, each set of air jet nozzles 382 is aimed at the open tops of one group or bank of cartridge filters 378. The air jet nozzles 392 associated with each bank of cartridge filters 378 are connected by air lines 398 to a pneumatic valve 400, which, in turn, is connected to the source 73 of pressurized air. In response to a signal from the system controller 108, the pneumatic valves 400 are operated to selectively direct pressurized air through air lines 398 so that a jet of pressurized air is emitted from the air jet nozzles 392 into the interior of one or both of the banks of cartridge filters 378. These pulsed jets of air dislodge powder coating material from the walls of the cartridge filters 378 so that it can fall by gravity into the powder collection chamber 374 and onto the porous plate 376. With reference to Figs. 1 and 7, air entrained powder coating material is drawn into each of the powder collection units 346 from the booth interior 30 under the application of a negative pressure exerted by the blower units 348 mentioned above. Each of the blower units 348 includes a fan plenum 402 which houses a fan or blower 404 and a number of final filters 406 depicted schematically in Fig. 1. The fan plenum 402 is formed with a number of openings 408 over which an exhaust duct 410 is fixedly mounted. Each exhaust duct 410 extends vertically upwardly into engagement with a coupling 412 located at the base of one of the extensions 373 of the clean air chambers 364 associated with each powder collection unit 346. In response to the operation of blower 404 within fan plenum 402, a negative pressure is developed within the exhaust duct 410 and, in turn, within the clean air chamber 364 associated with each of the powder collection units 346. This negative pressure creates a downwardly directed flow of air in the booth interior 30 within which oversprayed powder coating material is entrained. The air entrained powder coating material passes through the gratings 38 at the floor 20 of the spray booth 12 and enters each of the powder collection units 346 where the powder coating material is collected along the walls of the cartridge filters 378 or falls onto the porous plate 376 at the base of collector housing 350. An important aspect of the powder collection and recovery system 16 of this invention is that one blower unit 348 services a limited number of powder collection units 346. For example, the blower unit 348A depicted on the right hand portion of Fig. 7 has a fan plenum 402 formed with four openings 408 each of which receive an exhaust duct 410 connected to one powder collection unit 346. Accordingly, four powder collection units 346 are accommodated by one blower unit 348A. Other blower units 348 are associated with relatively small groups of adjacent powder collection units 346 which results in the application of a uniform, downwardly directed flow of air throughout the booth interior 30. Further, the configuration of the clean air chamber extensions 373 of each powder collection unit 346 permits the powder collection units 346 on one side of spray booth 12 to "dovetail" or fit closely adjacent the powder collection units 346 on the opposite side of booth 12. See center of Fig. 7. This conserves space and reduces the overall dimension of the booth 12. Another aspect of the powder collection and recovery system 16 of this invention is the retrieval of collected, oversprayed powder from the powder collection units 346 for recirculation back to the powder kitchen 14. As mentioned above, air entrained powder material from the booth interior 30 is drawn into each of the powder collection units 346 and falls either by gravity onto the porous plate 376 at the base thereof or is dislodged from the walls of the cartridge filters 378 by periodic bursts of pressurized air emitted from the air jet nozzles 392. In the presently preferred embodiment, movement of the powder onto the porous plate 376 is assisted by the forming of the walls 354-362 of the collector housing 350 of each powder collection unit 346 of a relatively thin gauge metal, such as 18-20 gauge No. 304 stainless steel, so that they vibrate when the reverse jets of pressurized air are emitted from air jet nozzles 392. Because the porous plate 376 is angled at about five degrees with respect to horizontal, the fluidized powder coating material thereon flows toward an outlet 422 on one side of the collector housing 350 at the lower end of porous plate 376. In turn, each of the outlets 422 of powder collection units 346 is connected by a branch line 424 to a common header pipe 426 which extends longitudinally along the length of powder booth 12 on both sides thereof. The header pipe 426 is connected to the reclaim line 86 which leads to the third powder receiver 82 within the powder kitchen 14. Preferably, a guillotine-type gate valve 428 is carried within each branch line 424, and these valves 428 are movable between an open position to permit the flow of powder coating material therethrough and a closed position to prevent such flow. in ' response to activation of the third vacuum pump 84 within the powder kitchen 14 , which is associated with third powder receiver 82 and reclaim hopper 80 as described above, a negative pressure is produced within the header pipe 426. The system controller 108, mentioned above in connection with the powder transfer system, is operative to selectively open the gate valves 428 associated with each powder collection unit 346 so that the powder therein is drawn through their respective branch lines 424 into header pipe 426. Because of the large number of powder collection units 346, only a predetermined number of gate valves 428 are opened at any given time to limit the total amount of powder material which is allowed to enter the header pipe 426 for transfer to the reclaim line 86 leading to the third powder receiver 82 and primary hopper 80. With reference to Fig. 1, a pressure sensor 430 is schematically depicted as being connected to the fan plenum 402 of the blower unit 348. The purpose of pressure sensor 430 is to sense the pressure drop across final filters 406 within blower unit 348 and send a signal representative of same to the controller 108. In the event of a failure or other problem with one or more cartridge filters 378 within the powder collection unit 346 associated with a given blower unit 348, the passage of powder coating material into the clean air chamber 364 and then to the final filters 406 creates a pressure drop across the final filters 406. This pressure drop is sensed by the pressure sensor 430 at which time a signal representative of such pressure drop is sent to the controller 108 to alert the operator of a problem within such powder collection unit 346. Because there are a number of blower units 348, each associated with a group of powder collection units 346, a failure within the powder collection and recovery system 16 can be pinpointed and attributed to one blower unit 348 and an associated group of powder collection units 346. This facilitates maintenance of the system and avoids the operator having to check each of the blower units 348 for such problems. While the invention has been described with reference to a preferred embodiment, it should be understood by those skilled in the art that various changes may be made and equivalence may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. For example, the system 10 of this invention has been depicted with a single primary hopper 60, a single reclaim hopper 80, a feed hopper 68 associated with a robot hopper 78 and robot 40, and, a feed hopper 96 associated with an overhead gun manipulator 44. It should be understood that the embodiment of system 10 depicted in the Figs, and described above is intended for purposes of illustration of the subject matter of this invention, and that the system 10 could be modified depending upon the requirements of a particular application. Multiple primary hoppers 60 and reclaim hoppers 80 can be employed, and a variety of spray gun configurations can be utilized including automatically and manually manipulated guns supplied with different combinations of feed hoppers and/or robot hoppers. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. We claim:

Claims: 1. Apparatus for applying powder coating material onto objects transmitted through a powder spray booth, comprising: a primary hopper containing powder coating material, a feed hopper; first transfer means, connected between said primary hopper and said feed hopper, for transmitting powder coating material under the application of negative pressure from said primary hopper to said feed hopper; second transfer means for transmitting power coating material from said feed hopper to dispensing devices associated with the powder spray booth. 2. The apparatus of claim 1 in which said primary hopper is located at a remote position relative to said feed hopper. 3. The apparatus of claim 1 in which said feed hopper is separated a substantial distance from said primary hopper and is adapted to be located in a position close to the powder spray booth compared to said primary hopper. 4. The apparatus of claim 1 in which said second transfer means is a powder pump connected to said feed hopper, said powder pump being effective to transfer by positive pressure the powder coating material within said feed hopper to dispensing devices associated with the powder spray booth. 5. The apparatus of claim 1 further including a third transfer means, connected to said primary hopper, for transmitting coating material under the application of negative pressure from a source of powder coating material to said primary hopper. 6. The apparatus of claim 5 in which said third transfer means comprises: a powder receiver unit including a powder collection chamber connected to the source of powder coating material; means for transferring powder coating material from the source into said powder collection chamber under the influence of negative pressure; means for transferring a metered quantity of powder coating material from said powder collection chamber into said primary hopper. 7. The apparatus of claim 6 in which said second transfer means comprises: a powder receiver unit including a powder collection chamber connected to said primary hopper; means for transferring powder coating material from said primary hopper into said powder collection chamber under the influence of negative pressure; means for transferring a metered quantity of powder coating material from said powder collection chamber into said feed hopper. 8. The apparatus of claim 7 in which said powder receiver unit of each of said second and third transfer means includes a clean air chamber separated from said powder collection chambers thereof, at least one cartridge filter being located within said powder collection chambers and in communication with said clean air chambers, and means for dislodging powder coating material collected on said cartridge filter. 9. The apparatus of claim 7 in which said means for transferring powder coating material into said powder collection chamber of said powder receiver units of each of said second and third transfer means comprises a vacuum pump connected to their respective powder collection chambers which is effective to create a negative pressure to draw powder into said powder collection chambers. 10. The apparatus of claim in which said means for transferring a metered quantity of powder coating material associated with each of said powder receiver units comprises: a metering air lock connected to said powder collection chamber; and a sieve connected between said metering air lock and said primary hopper or said feed hopper. 11. The apparatus of claim 1 further including: a transfer line interconnecting said primary hopper and said feed hopper; first valve means, mounted in said transfer line, for turning on and off the flow of powder coating material from said primary hopper to said feed hopper; second valve means, connected to said transfer line downstream from said first valve means, for introducing air into said transfer line when said first valve means turns off the flow of powder coating material so that the powder coating material remaining in said transfer line downstream from said first valve means is transmitted into said feed hopper. 12. The apparatus of claim 1 in which said third transfer means comprises a gun supply hopper located proximate the powder spray booth and connected between said feed hopper and at least one powder spray device associated with the powder spray booth, and a pump connected to said feed hopper which is effective to transmit powder coating material from said powder collection into said gun supply hopper under the application of a positive pressure. 13. Apparatus for applying powder coating material onto objects transmitted through a powder spray booth within which a portion of the powder coating material fails to adhere to the objects and forms oversprayed powder coating material, comprising: a primary hopper containing virgin powder coating material, and at least one secondary hopper; a first feed hopper adapted to supply powder coating material to at least one spraying device associated with the powder spray booth; first transfer means for transmitting virgin powder coating material under the application of negative pressure from said primary hopper into said first feed hopper; second transfer means for transmitting oversprayed powder coating material collected within the powder spray booth, under the application of negative pressure, into one of said primary hopper and said at least one secondary hopper. 14. The apparatus of claim 13 in which said first transfer means comprises: a first powder receiver unit connected between the source of powder coating material and said primary hopper, said first powder receiver unit having a powder collection chamber communicating with said primary hopper; a first vacuum pump connected to said powder collection chamber of said first powder receiver unit to create a negative pressure therein which draws powder coating material from the source into said first powder receiver; a second powder receiver unit connected between said primary hopper and said first feed hopper, said second powder receiver unit having a powder collection chamber communicating with said first feed hopper; a second vacuum pump connected to said powder collection chamber of said second powder receiver unit to create a negative pressure therein which draws powder coating material from said primary hopper into said second powder receiver. 15. The apparatus of claim 13 in which said at least one secondary hopper is a reclaim hopper, said reclaim hopper being connected to a second feed hopper adapted to supply powder coating material to at least one spraying device associated with the powder spray booth. 16. The apparatus of claim 15 in which said second transfer means comprises: a second powder receiver unit adapted to be connected between the powder spray booth and said reclaim hopper, said second powder receiver unit having a powder collection chamber communicating with said reclaim hopper; a second vacuum pump connected to said powder collection chamber of said second powder receiver unit to create a negative pressure therein which draws oversprayed powder coating material from the powder spray booth into said second powder receiver; a third powder receiver unit connected between said reclaim hopper and said second feed hopper, said third powder receiver unit having a powder collection chamber communicating with said third feed hopper; a third vacuum pump connected to said powder collection chamber of said third powder receiver unit to create a negative pressure therein which draws powder coating material from said reclaim hopper into said third powder receiver. 17. The apparatus of claim 13 in which said at least one secondary hopper is a reclaim hopper which receives oversprayed powder material from said second transfer means, said apparatus further including a third transfer means for selectively transferring virgin powder coating material from said primary hopper into said reclaim hopper to supplement the supply of powder coating material thereto. 18. The apparatus of claim 17 in which said third transfer means includes: sensing means for sensing the quantity of oversprayed powder coating material present within said reclaim hopper, and for producing a signal representative thereof; pump means, connected to said primary hopper, for pumping virgin powder coating material from said primary hopper to said reclaim hopper dependent on said signal. 19. The apparatus of claim 18 in which said sensing means is a load cell which supports said reclaim hopper, said load cell being effective to sense changes in weight of the powder coating material within said reclaim hopper, corresponding to changes in the quantity of powder coating material therein, and to produce said signal in the event the weight of powder coating material within said reclaim hopper falls below a predetermined level. 20. Apparatus for applying powder coating material onto objects transmitted through a powder spray booth within which a portion of the powder coating material fails to adhere to the objects and forms oversprayed powder coating material, comprising: a powder kitchen which houses at least one primary hopper containing virgin powder coating material, and at least one secondary hopper; a first feed hopper adapted to be located proximate to the powder spray booth in comparison to said powder kitchen, said feed hopper being adapted to supply powder coating material to powder spray guns associated with the powder spray booth; transfer means, operating under the application of negative pressure, for transferring oversprayed powder coating material from the powder spray booth to one of said primary and said at least one secondary hoppers, and for transferring powder coating material from one of said primary hopper and said at least one secondary hoppers to said first feed hopper. 21. The apparatus of claim 20 in which said powder kitchen is an enclosure having an interior which is substantially isolated from ambient air. 22. The apparatus of claim 20 in which said at least one secondary hopper is a reclaim hopper adapted to be connected to the powder spray booth, and wherein said apparatus further includes a second feed hopper connected to said reclaim hopper. 23. The apparatus of claim 22 in which said transfer means comprises: an individual powder receiver unit associated with each of said primary hopper, said reclaim hopper and said first and second feed hoppers, each of said powder receiver units including means for (i) receiving powder coating material from one of the source of virgin powder coating material, the powder spray booth or another hopper, and for (ii) transmitting metered quantities of powder coating material to their associated hoppers; vacuum means, connected to each of said powder receiver units, for transferring powder coating material into said powder receiver units under the application of negative pressure. 24. The apparatus of claim 23 in which each of said powder receiver units comprises: a powder collection chamber for receiving powder coating material, said powder collection chamber containing a cartridge filter; a clean air chamber separated from said powder collection chamber; air jet means for dislodging powder coating material from said cartridge' filter; means for transmitting a metered quantity of powder coating material from said powder collection chamber into an associated hopper. 25. The apparatus of claim 24 in which said means for transferring a metered quantity of powder coating material associated with each of said powder receiver units comprises: a metering air lock connected to said powder collection chamber; and a sieve connected between said metering air lock and said primary hopper, said reclaim hopper or said first and second feed hoppers. 26. Apparatus for applying powder coating material onto objects transmitted through a powder spray booth, comprising: a primary hopper for receiving powder coating material, first transfer means, connected to said primary hopper, for transmitting powder coating material to said primary hopper; first means for sensing the quantity of powder coating material within said primary hopper, and for causing, said first transfer means to transmit powder coating material into said primary hopper when said quantity of powder coating material falls below a predetermined amount; a feed hopper; second transfer means, connected between said primary hopper and said feed hopper, for transmitting powder coating material under the application of negative pressure from said primary hopper to said feed hopper; second means for sensing the quantity of powder coating material within said feed hopper, and for operating said second transfer means when said quantity of powder coating material falls below a predetermined amount. 27. The apparatus of claim 26 in which said first means is a load cell which supports said primary hopper, said load cell being effective to sense changes in weight of the powder coating material within said primary hopper, corresponding to changes in said quantity of powder coating material therein, and to produce a signal in the event said weight falls below a predetermined level, said load cell transmitting said signal to a control means which operates said first transfer means to supply powder coating material to said primary hopper. 28. The apparatus of claim 27 in which said second means is a load cell which supports said feed hopper, said load cell being effective to sense changes in weight of the powder coating material within said feed hopper, corresponding to changes in said quantity of powder coating material therein, and to produce a signal in the event said weight falls below a predetermined level, said load cell transmitting said signal to a control means which operates said second transfer means to supply powder coating material to said feed hopper. 29. The apparatus of claim 28 in which each of said first and second transfer means includes a powder receiver unit coupled to said primary hopper or to said feed hopper, said powder receiver units being supported independently of said primary hopper and said feed hopper so that said load cells associated therewith measure only the weight of powder coating material entering said primary and feed hoppers. 30. Apparatus for supplying powder coating material, comprising: a hopper housing having an interior including an internal wall which forms a first powder fluidizing area and a second powder fluidizing area; a porous plate carried within said hopper housing which divides said interior thereof into a fluidized bed located above said porous plate and an air plenum below said porous plate, said hopper housing being formed with a powder inlet for introducing powder coating material into said fluidizing bed and an air inlet for introducing an upward flow of air into said air plenum beneath said porous plate; first agitator means located within said first powder fluidizing area and second agitator means located within said second powder fluidizing area, for creating a stable, fluidized bed of powder within said first and second fluidizing areas, respectively. 31. The apparatus of claim 30 in which said internal wall of said hopper housing is formed in the general shape of a figure 8 with two substantially circular portions which meet at a center area of reduced diameter. 32. The apparatus of claim 31 in which said internal wall of said housing includes opposed, triangular shaped baffles which form said center area of reduced diameter. 33. The apparatus of claim 30 in which each of said first and second agitator means includes a motor driver paddle located within one of said first and second fluidizing areas above said porous plate, one of said paddles being positioned vertically above and overlapping the other of said paddles. 34. The apparatus of claim 30 wherein a portion of the powder coating material introduced into said interior of said hopper housing includes fines, said apparatus further including a vent connected to a vent collector operative to remove said fines from said interior of said hopper housing. 35. The apparatus of claim 30 in which said air plenum includes baffles to direct an evenly distributed flow of air upwardly to said porous plate. 36. Apparatus for applying powder coating material onto objects, comprising: a spray booth having a ceiling, floor, and opposed side walls defining an interior which provides a controlled area for the application of powder coating material onto objects moving therethrough; powder collection means located immediately adjacent said spray booth for collecting oversprayed powder from said interior thereof, said powder collection means including: (i) powder collection units extending along substantially the length of said spray booth, each of said powder collection units having a powder collection chamber for receiving oversprayed powder from said interior of said spray booth; (ii) a clean air chamber associated with each of said powder collection units, each of said clean air chambers having an interior which is isolated from the oversprayed powder entering said powder collection chamber; (iii) filter means located within each of said powder collection chambers and connected to said clean air chambers for collecting oversprayed powder thereon to form clean air which is introduced into said clean air chambers; a number of exhaust units, each connected to at least one powder collection unit, for creating a negative pressure within said powder collection chambers connected thereto to draw air entrained powder coating material from said spray booth into said powder collection units. 37. The apparatus of claim 36 in which each of said powder collection units is connected by a connector line to a common header pipe, each of said connector lines carrying a valve movable between an open position and a closed position. 38. The apparatus of claim 37 further including means for applying a negative pressure within said common header pipe, and means for sequentially opening and closing said valves associated with each of said powder collection units. 39. The apparatus of claim 36 in which each of said exhaust units includes an exhaust plenum and an exhaust fan, said exhaust plenum being connected by separate duct to said clean air chamber of each of said at least one powder collection unit, said exhaust fan being operative to create a negative pressure within each of said at least one powder collection unit through said exhaust plenum and said ducts. 40. The apparatus of claim 39 in which each of said exhaust plenums includes a number of final filters and means for sensing the pressure drop across said final filters. 41. The apparatus of claim 36 in which said powder collection chamber of each of said powder collection units includes a porous plate mounted at an angle relative to horizontal in position to receive powder coating material from said spray booth, said powder collection chamber being formed with an air inlet for directing a flow of air through said porous plate to fluidize powder coating material received thereon. 42. The apparatus of claim 36 in which said filter means includes two banks of cartridge filters mounted in an inverted V-shape within said powder collection chamber of each powder collection unit. 43. The apparatus of claim 42 further including a number of reverse air jet valves mounted within said clean air chamber of each powder collection unit in position above said cartridge filters, each of said reverse air jet valves being positioned in alignment with one of said cartridge filters. 44. Apparatus for supplying powder coating material comprising: a hopper housing having an interior formed by a top wall, sidewall and bottom wall; a porous plate carried within said hopper housing which divides said interior thereof into a fluidized bed located above said porous plate and an air plenum below said porous plate, said hopper housing being formed with a powder inlet for introducing powder coating material into said fluidizing bed and an air inlet for introducing an upward flow of air into said air plenum beneath said porous plate; and a vertically oriented baffle located within said fluidized bed between said top wall of said hopper housing and said porous plate, said baffle being located between said powder inlet and a powder discharge tube extending into said interior of said hopper housing. 45. The apparatus of claim 44 further including agitator means for creating a stable area of fluidized powder in the vicinity of said discharge tube. 46. The apparatus of claim 44 in which said discharge tube within said hopper housing is connected to a robot carrying at least one powder spray gun. 47. Apparatus for applying powder coating material onto objects, comprising: a spray booth having a floor, ceiling and opposed side walls defining an interior which provides a controlled area for the application of powder coating material onto objects moving therethrough; a number of powder collection units located immediately adjacent said spray booth for collecting oversprayed powder from said interior thereof; control means for sequentially transferring the oversprayed powder coating material, under the application of negative pressure, from said powder collection units to a common header pipe; means for transferring the oversprayed powder coating material, under the application of negative pressure, from said common header pipe to a hopper. 48. The apparatus of claim 47 in which each of said powder collection units is connected by a connector line to said common header pipe, said control means including a gate valve mounted within each of said connector lines to control the flow of powder coating material therethrough. 49. The apparatus of claim 47 in which each of said powder collection units includes a powder collection chamber, each of said powder collection chambers including a porous plate mounted at an angle relative to horizontal in position to receive powder coating material from said spray booth, said powder collection chambers each being formed with an air inlet for directing a flow of air through said porous plate to fluidize powder coating material received thereon. 50. A method of applying powder coating material onto objects moving through a powder spray booth, comprising: transmitting powder coating material under the application of negative pressure from a primary hopper containing the powder coating material to a feed hopper; transmitting powder coating material from the feed hopper to at least one powder spray device associated with the powder spray booth. 51. The method of claim 50 further including the step of transmitting powder coating material under the application of negative pressure from a source into the primary hopper. 52. The method of claim 51 in which said step of transmitting powder coating material under the application of negative pressure from a source into the primary hopper includes transmitting the powder coating material from the source into the powder collection chamber of a powder receiver unit associated with the primary hopper, and then transferring a metered quantity of the powder coating material from the powder collection chamber into the primary hopper. 53. The method of claim 52 in which said step of transferring a metered quantity of powder coating material comprises operating an air lock metering device connected to the powder collection chamber to transfer a metered quantity of powder coating material therefrom to a sieve coupled to the primary hopper. 54. The method of claim 50 in which said step of transmitting powder coating material under the application of negative pressure from the primary hopper into the feed hopper includes transmitting the powder coating material from the primary hopper into the powder collection chamber of a powder receiver unit associated with the feed hopper, and then transferring a metered quantity of the powder coating material from the powder collection chamber into the feed hopper. 55. The method of claim 54 in which said step of transferring a metered quantity of powder coating material comprises operating an air lock metering device connected to the powder collection chamber to transfer a metered (quantity of powder coating material therefrom to a sieve coupled to the feed hopper. 56. The method of claim 50 in which said step of transmitting powder coating material from the feed hopper to at least one powder spray device comprises pumping powder coating material under the application of positive pressure to the spray device. 57. The method of claim 50 in which said step of transmitting powder coating material from the feed hopper to at least one powder spray device comprises pumping powder coating material under the application of positive pressure to a robot hopper associated with a robot operative to manipulate one or more spray devices within the powder spray booth. 58. A method of applying powder coating material onto objects moving through a powder spray booth, comprising: transmitting powder coating material under the application of negative pressure from a primary hopper to a first feed hopper located proximate the powder spray booth; transmitting oversprayed powder coating material under the application of negative pressure from a powder collection and recovery system associated with the powder spray booth into one of a primary hopper and a secondary hopper; transmitting the oversprayed powder coating material under the application of negative pressure from said one of the primary and secondary hoppers to a second feed hopper located proximate the powder spray booth; transmitting powder coating material from the first and second feed hoppers to separate powder spray devices associated with the powder spray booth. 59. The method of claim 58 in which said step of transmitting oversprayed powder coating material under the application of negative pressure from a powder collection and recovery system comprises: collecting oversprayed powder coating material in a number of individual powder collection units associated with the powder spray booth; sequentially transferring the collected, oversprayed powder coating material from the powder collection units into a common header pipe; and transferring the oversprayed powder coating material from the header pipe into said one of the primary and secondary hoppers. 60. The method of claim 59 in which said step of sequentially transferring the collected, oversprayed powder coating material comprises sequentially opening gate valves carried within connector lines extending between each of the powder collection units and the common header pipe. 61. The method of claim 58 in which said step of transmitting oversprayed powder coating material under the application of negative pressure from a powder collection and recovery system comprises transmitting the oversprayed powder coating material into a reclaim hopper separate from the primary hopper. 62. The method of claim 61 in which said step of transmitting powder coating material from the first and second feed hoppers comprises transmitting virgin powder coating material supplied to the first feed hopper by the primary hopper to powder spray devices, and transmitting oversprayed powder coating material supplied to the second feed hopper by the reclaim hopper to powder spray devices. 63. A method of applying powder coating material onto objects moving through a powder spray booth, comprising: transmitting powder coating material under the application of negative pressure from a primary hopper to a feed hopper located proximate the powder spray booth; transmitting powder coating material from the feed hopper to at least one powder spray device associated with the powder spray booth; monitoring the quantity of powder coating material within the feed hopper, and transmitting additional powder coating material from the primary hopper into the feed hopper whenever the quantity of powder coating material within the feed hopper falls below a predetermined level. 64. The method of claim 53 in which said step of monitoring the weight of powder coating material within the feed hopper comprises monitoring signals representative of the weight of powder coating material within the feed hopper produced by a load cell which supports the feed hopper, and activating a transfer means to supply powder coating material to the feed hopper under the application of negative pressure in response to the signals. 65. The method of claim 63 further including the step of transmitting powder coating material from a source into the primary hopper. 66. The method of claim 65 in which said step of transmitting the powder coating material from the source includes: monitoring the weight of powder coating material within the primary hopper; and transmitting additional powder coatingmaterial from the source into the primary hopper whenever the weight of powder coating material within the primary hopper falls below a predetermined level. 67. A method of applying powder coating material onto objects moving through a powder spray booth, comprising: transmitting virgin powder coating material under the application of negative pressure from a primary hopper to a first feed hopper located proximate the powder spray booth; transmitting oversprayed powder coating material under the application of negative pressure from a powder collection and recovery system associated with the powder spray booth into a reclaim hopper positioned at a remote location from the powder spray booth; transmitting the oversprayed powder coating material under the application of negative pressure from the reclaim hopper to a second feed hopper located proximate the powder spray booth; transmitting virgin powder coating material from the first feed hopper and oversprayed powder coating material from the second feed hopper to separate powder spray devices associated with the powder spray booth; monitoring the weight of virgin powder coating material within the first feed hopper, and transmitting additional virgin powder coating material from the primary hopper into the first feed hopper whenever the weight of virgin powder coating material within the first feed hopper falls below a predetermined level; and monitoring the weight of oversprayed powder coating material within the second feed hopper, and transmitting additional oversprayed powder coating material from the reclaim hopper into the second feed hopper whenever the weight of oversprayed powder coating material within the second feed hopper falls below a predetermined level. 68. The method of claim 67 further including the step of monitoring the weight of oversprayed powder coating material within the reclaim hopper. 69. The method of claim 68 in which said step of monitoring the weight of oversprayed powder coating material within the reclaim hopper further includes transferring virgin powder coating material from the primary hopper into the reclaim hopper in the event sufficient oversprayed powder coating material is not available from the powder collection and recovery system of the powder spray booth. 70. A method of collecting and recovering oversprayed powder coating material from the interior of a powder spray booth, comprising: creating a negative pressure within the interior of the powder spray booth; drawing air entrained powder coating material from the booth interior into a number of individual powder collection units located beneath the floor of the powder spray booth; sequentially transferring the oversprayed powder coating material, under the application of negative pressure, from the powder collection units into a common header pipe; transferring the oversprayed powder coating material, under the application of negative pressure, from the common header pipe to a hopper. 71. The method of claim 70 in which said step of creating a negative pressure within the interior of the powder spray booth comprises activating a number of individual blower units each associated with at least one powder collection unit, each blower unit being effective to create a negative pressure within its associated powder collection unit and within the booth interior. 72. The method of claim 70 in which said step of sequentially transferring the collected, oversprayed powder coating material from the powder collection units comprises sequentially opening gate valves each carried within a connector line extending between one of the powder collection units and the common header pipe.

Inventors: CARLSON JOHN F, FENA ERNEST J, HOLLSTEIN THOMAS E, SHUTIC JEFFREY R, WILLIAMS KEITH E, CARLSON, JOHN, F., FENA, ERNEST, J., HOLLSTEIN, THOMAS, E., SHUTIC, JEFFREY, R., WILLIAMS, KEITH, E.
Applicants: NORDSON CORP, NORDSON CORPORATION
Application year: 1994
Main classification: B05B15
IPC codes: B05B7, B05B12, B05B15, B05D1, B65G53